The relationship between functional driving performance and age, senile dementia of the Alzheimer type (SDAT), and deficits in specific cognitive aspects related to attentional processing, visuoperceptual function, and motor control remain largely unexplored. This study will assess longitudinally the driving performance of subjects with very mild (N=60) and mild (N=60) SDAT who continue to drive as compared with healthy elderly control drivers (N=60). All participants will be recruited from the Washington University Alzheimer's Disease Research Center (ADRC) where clinical staging of dementia and full neuropsychological testing are performed annually. The functional assessment tool will be an in-car, on-the-road driving evaluation which has been successfully piloted in this population. Subject self-report of driving ability and an independent assessment of driving behaviors by a collateral source also will be obtained. Independent verification of crashes and citations will be sought from the responsible state agencies in Missouri and Illinois. Driving performance will be measured by the on-the-road evaluation every 6 months in subjects who passed the previous assessment. In subjects who did not pass or who do not return for re-examination, history of driving behaviors (including cessation of driving) will be obtained from the collateral source. At entry and at specified intervals thereafter, all participants will undergo a battery of tests to measure vigilance, selective attention, divided attention, attentional capacity, and useful field of view. Additionally, through separately funded RO-1 projects in the ADRC, all subjects will be studied annually for visuoperceptual function (including motion discrimination and high spatial frequency contrast sensitivity) and motor control processes (motor plan preparation and execution). This study will characterize driving performance in normal aging and in persons with SDAT. It also will identify cognitive and attentional factors that are associated with retained driving skills to guide development of screening instruments and will measure performance over time. It will provide information useful for public policy decisions regarding driving competency and re-licensing intervals for these populations.